CN116405185B

CN116405185B - Free-space orbital angular momentum broadcast communication system based on all-optical chaotic modulation

Info

Publication number: CN116405185B
Application number: CN202310392513.0A
Authority: CN
Inventors: 江宁; 张逸群; 张强; 邱昆
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2023-04-12
Filing date: 2023-04-12
Publication date: 2025-09-30
Anticipated expiration: 2043-04-12
Also published as: CN116405185A

Abstract

The invention discloses a free space orbital angular momentum broadcast communication system based on full-optical chaotic modulation, which is characterized in that a main laser in an encryption transmitting end generates a broadband chaotic carrier signal through a conventional optical feedback structure, optical information is hidden in a chaotic optical carrier wave for encryption through an intensity modulation mode, a specially designed multi-order multiplexing phase plate is loaded on a spatial light modulator in an optical field regulation module, gaussian encrypted optical signals collimated into a spatial light path are regulated and controlled into multiplexing light beams with a plurality of OAM modes, a plurality of opposite single-order phase plates are respectively loaded on the spatial light modulator in the OAM broadcasting module after the transmission of a free space link, relevant optical field mode demodulation is realized, the signals respectively correspond to a plurality of users at a receiving end, local chaotic synchronization is realized by the users through a unidirectional injection-locking mechanism in the receiving module, and original information is obtained through subtracting the chaotic optical carrier wave carrying the information from the local synchronous chaotic signal, and finally the safe broadcast communication is completed.

Description

Free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation

Technical Field

The invention belongs to the technical field of optical communication, and particularly relates to a free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation.

Background

In recent years, with the vigorous development of technologies such as 4G/5G mobile communication, internet of things, cloud computing, big data, artificial intelligence and the like, more convenience is brought to life of people, and more challenges are brought to a communication system. As one of the main modes of information transmission, optical communication technology is evolving from multichannel, high-speed to ultra-high-speed, ultra-large-capacity, and ultra-long-distance optical communication.

The space laser communication has the outstanding advantages of high speed, strong electromagnetic interference resistance, no spectrum limitation and the like, is a scene core communication system such as 'last kilometer communication', star-to-ground/inter-star communication and the like, and meanwhile, vortex beams carrying different Orbital Angular Momentum (OAM) modes have the characteristic of being orthogonal to each other, so that the transmission capacity of the space laser communication system can be further improved through multiplexing, broadcasting and the like. However, with the rapid increase of the transmission capacity, the information security problem is becoming more serious, especially when the laser beam diverges after being transmitted through a long-distance free space channel, so that the spot size of the receiving end is enlarged, and the risk of eavesdropping is greatly increased.

At present, the traditional information security technology mostly adopts the cryptography encryption algorithm technology to encrypt data at a medium access control layer and an upper layer thereof, and with the advent of a quantum computer with ultra-fast computing capability, the secret communication mode based on algorithm encryption faces the threat of being cracked by violence, while the physical layer security is used as a first barrier of the security of the whole communication system, thereby having important significance. Therefore, how to improve the physical layer information security of the free space optical communication system has become a research hot problem in the current academia.

The chaotic signal generated based on the nonlinear dynamics characteristic of the laser has the characteristics of initial value sensitivity, broadband noise and the like, can mask information in a broadband chaotic light carrier wave to realize secret light transmission, and is one of important technologies for enhancing the information security of a physical layer of an optical communication system. However, after intensive research, the scholars find that the inherent relaxation oscillation of the semiconductor laser leads to the chaotic laser bandwidth being only several GHz, in chaotic optical communication, the chaotic laser is used as optical information of carrier hiding transmission, and the limited chaotic carrier bandwidth limits the transmission rate of the chaotic optical communication, and although some laser chaotic bandwidth enhancement schemes have been proposed, the scheme is difficult to apply to the existing optical communication system due to the complexity of the scheme.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, and provides a free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation, which ensures the transmission safety of an optical information space link, utilizes the space dimension of a chaotic carrier wave and improves the transmission capacity of the chaotic communication system.

The invention provides a free space orbital angular momentum broadcast communication system based on full-optical chaotic modulation, which is characterized by comprising an encryption transmitting end, an optical field regulating module, a free space link, an OAM broadcast module and a receiving user end;

The encryption transmitting end comprises a main laser DL, a polarization controller PC, an optical fiber coupler FC1, an adjustable optical attenuator VOA1, an optical fiber reflector M1, an optical isolator ISO, a Mach-Zehnder modulator MZM and an arbitrary waveform generator AWG;

the method comprises the steps that a main laser DL generates a laser signal, the laser signal is input to an optical fiber coupler FC1 after passing through a polarization controller PC, the optical fiber coupler FC1 divides laser into two paths according to a set light splitting ratio, one path of light is reflected back to the main laser DL by an optical fiber reflector M1 after being attenuated by an adjustable optical attenuator VOA1, the other path of light is output into a chaotic light carrier, the chaotic light carrier enters a Mach-Zehnder modulator MZM after passing through an optical isolator ISO, meanwhile, information generated by an arbitrary waveform generator AWG is modulated onto the chaotic light carrier through the MZM to obtain a chaotic light carrier carrying information, and the chaotic light carrier is collimated into a space Gaussian beam by an optical fiber collimator COL1 to enter a light field regulation module;

The light field regulation module comprises a linear polaroid LP and a reflective spatial light modulator SLM1;

The chaotic light carrier wave carrying information is transmitted to a reflective spatial light modulator (SLM 1) to regulate and control an n-order multiplexing light field of OAM after passing through a Linear Polarizer (LP), and the regulated and controlled light signal is reflected to a free space link for transmission through the reflective spatial light modulator (SLM 1) and then enters an OAM broadcasting module;

The OAM broadcasting module comprises a spatial light modulator SLM2, n 45-degree reflectors M2-1-M2-n and n optical fiber collimators COL 2-1-COL 2-n;

Dividing a liquid crystal screen of a spatial light modulator SLM2 into n parts, wherein each part corresponds to a receiving user, and each user loads a vortex phase plate with opposite orders on the corresponding part of the liquid crystal screen to demodulate OAM (operation administration and maintenance) of the user to obtain n paths of Gaussian beams after demodulation, wherein the first path of Gaussian beam enters an optical fiber through a reflector M2-1 and an optical fiber collimator COL2-1 to be transmitted to the receiving user 1, the second path of demodulated Gaussian beam enters the optical fiber through M2-2 and COL2-2 to be transmitted to the receiving user 2, and the like, so that broadcasting of n users based on the OAM is realized;

The receiving user side comprises n receiving users with the same structure, wherein the ith receiving user comprises an optical fiber isolator ISO, a small signal amplifier EDFA, a 2X 2 optical fiber coupler FC2-i, three adjustable optical attenuators VOA2-i/VOA3-i/VOA4-i, a polarization controller PC, a slave laser SL _i and two photodetectors PD1-i/PD2-i, i=1, 2,3,;

In the ith receiving user, the optical signal coupled by the collimator is input to the small signal amplifier EDFA after passing through the optical fiber isolator ISO, the small signal amplifier EDFA compensates space transmission damage and is divided into two paths by the optical fiber coupler FC2-i, one path of optical signal is unidirectionally injected to the slave laser SL _i through the adjustable optical attenuator VOA2-i and the polarization controller PC, at the moment, a local synchronous chaotic signal is generated from the laser SL _i and is received by the photoelectric detector PD2-i after passing through the optical fiber coupler FC2-i and the adjustable optical attenuator VOA4-i, the other path of optical signal is received by the photoelectric detector PD1-i after passing through the adjustable optical attenuator VOA3-i, and finally, the signals received by the two photoelectric detectors are subtracted to obtain the original optical signal.

The invention aims at realizing the following steps:

the invention discloses a free space orbital angular momentum broadcast communication system based on full-optical chaotic modulation, which comprises a main laser in an encryption transmitting end, a spatial light modulator, a multi-order multiplexing phase plate, a plurality of opposite single-order phase plates, a receiving end and a receiving module, wherein the main laser in the encryption transmitting end generates a broadband chaotic carrier signal through a conventional optical feedback structure and then conceals optical information in a chaotic optical carrier wave for encryption through an intensity modulation mode, the spatial light modulator in a light field regulation module is loaded with a specially designed multi-order multiplexing phase plate, gaussian encrypted optical signals collimated into a spatial light path are regulated and controlled into multiplexing light beams with a plurality of OAM modes, after the multiplexing light beams are transmitted through a free space link, the spatial light modulator in the OAM broadcasting module is respectively loaded with a plurality of opposite single-order phase plates to realize relevant light field mode demodulation and respectively correspond to a plurality of users at the receiving end, and the receiving module utilizes a unidirectional injection-locking mechanism to realize local chaotic synchronization, so that original information is obtained through subtracting the chaotic optical carrier wave carrying information from the local synchronous chaotic signal.

Meanwhile, the free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation has the following beneficial effects:

(1) The all-optical chaotic OAM broadcasting safety communication scheme designed by the invention can effectively realize encryption and decryption of information, and ensures the communication safety and privacy of users in a broadcasting network;

(2) The optical field regulation module at the transmitting end in the OAM broadcast network can realize OAM multiplexing optical field generation only by using one spatial optical phase modulator, so that the system cost is greatly reduced;

(3) Compared with the conventional broadband chaotic signal generation scheme, the scheme realizes the improvement of the transmission capacity of the chaotic secret communication system by regulating and controlling the spatial mode of the chaotic signal.

Drawings

FIG. 1 is a schematic diagram of a free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation;

Fig. 2 shows a time domain waveform diagram and a spectrogram of a master laser and a slave laser output signal, wherein (a 1) is a time domain waveform diagram of a master laser output signal, (a 2) is a time domain waveform diagram of a slave laser output signal, (b 1) is a spectrogram of a master laser output signal, (b 2) is a spectrogram of a slave laser output signal, and (c) is a cross-correlation diagram between two communication party output signals;

Fig. 3 is a diagram of a time domain waveform of information demodulated for a legal receiving user (a), a diagram of a time domain waveform of information demodulated for an illegal receiving user (b), a diagram of an information eye demodulated for a legal receiving user (c), and a diagram of an information eye demodulated for an illegal receiving user (d), taking the example of the user 1.

Detailed Description

The following description of the embodiments of the invention is presented in conjunction with the accompanying drawings to provide a better understanding of the invention to those skilled in the art. It is to be expressly noted that in the description below, detailed descriptions of known functions and designs are omitted here as perhaps obscuring the present invention.

Examples

Fig. 1 is a schematic diagram of a free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation.

In this embodiment, as shown in fig. 1, the free space orbital angular momentum broadcast communication system based on full-optical chaotic modulation of the invention comprises an encryption transmitting end, an optical field regulating module, a free space link, an OAM broadcast module and a receiving user end;

The main laser DL generates laser signals, the laser signals are input to the optical fiber coupler FC1 after passing through the polarization controller PC, the optical fiber coupler FC1 divides the laser into two paths according to the set optical splitting ratio, in the embodiment, the optical splitting ratio is set to be 2:8, one path of laser containing 20% is attenuated by the adjustable optical attenuator VOA1 and then reflected back to the main laser DL by the optical fiber reflector M1, the other path of laser containing 80% is output as a chaotic light carrier wave, the chaotic light carrier wave enters the Mach-Zehnder modulator MZM after passing through the optical isolator ISO, meanwhile, information generated by the arbitrary waveform generator AWG is modulated onto the chaotic light carrier wave through the MZM to obtain the chaotic light carrier wave with information, and the chaotic light carrier wave is collimated into a space Gaussian beam by the optical fiber collimator COL1 to enter the light field regulation module;

The OAM broadcasting module comprises a spatial light modulator SLM2, n 45-degree reflectors M2-1 to M2-n and n optical fiber collimators COL2-1 to COL2-n;

The receiving user side comprises n receiving users with the same structure, wherein the ith receiving user comprises an optical fiber isolator ISO, a small signal amplifier EDFA, a 2X 2 optical fiber coupler FC2-i, three adjustable optical attenuators VOA2-i/VOA3-i/VOA4-i, a polarization controller PC, a slave laser SL _i and two photodetectors PD1-i/PD2-i, i=1, 2,3, n;

Taking a user i as an example, in the ith receiving user, an optical signal coupled by a collimator is input into a small signal amplifier EDFA after passing through an optical fiber isolator ISO, the small signal amplifier EDFA compensates space transmission damage and is divided into two paths by an optical fiber coupler FC2-i, one path of optical signal is unidirectionally injected into a slave laser SL _i through an adjustable optical attenuator VOA2-i and a polarization controller PC, a local synchronous chaotic signal is generated from the laser SL _i at the moment and is received by a photoelectric detector PD2-i after passing through the optical fiber coupler FC2-i and the adjustable optical attenuator VOA4-i, the other path of optical signal is received by the photoelectric detector PD1-i after passing through the adjustable optical attenuator VOA3-i, and finally, the signals received by the two photoelectric detectors are subtracted to obtain an original optical signal.

Next, experimental verification results will be shown, and as a principle verification experiment, we successfully verify OAM broadcast security transmission of a signal with a single user bit rate of 6Gbps and a modulation format of OOK in a 1.2 m free space link. Taking the receiving user 1 as an example, fig. 2 shows a chaotic carrier time domain waveform diagram (a 1), a spectrogram (b 1) generated by the main laser DL, and a local chaotic signal time domain waveform diagram (a 2), a spectrogram (b 2) and a correlation point diagram (c) of the user 1 generated from the laser SL 1. Here we use the cross-Correlation Coefficient (CC) to quantify the correlation between their output signals. After OAM broadcasting provided by the scheme, the cross correlation coefficient is as high as 0.95, and the chaotic signals generated by the receiving end can be highly correlated with the chaotic signals generated by the transmitting end, so that the correct demodulation of the signals is ensured by the high correlation.

Fig. 3 shows the original information signal (a), the encrypted signal waveform (b) and the corresponding eye diagrams (c) and (d) of user 1. It can be seen that, compared with the open condition of the communication eye diagram of the original information signal, the encrypted information waveform shows a random fluctuation trend, the original information cannot be distinguished, the communication eye diagram is tightly closed, and the encryption error rate is close to 0.5 through calculation, so that the safety of the OAM broadcast safety communication scheme is verified.

While the foregoing describes illustrative embodiments of the present invention to facilitate an understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but is to be construed as protected by the accompanying claims insofar as various changes are within the spirit and scope of the present invention as defined and defined by the appended claims.

Claims

1. The free space orbital angular momentum broadcast communication system based on all-optical chaotic modulation is characterized by comprising an encryption transmitting end, an optical field regulating module, a free space link, an OAM broadcast module and a receiving user end;